Deadlock reproducer

zvol.c.patch

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index fa5c7eb..0b318d4 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -46,6 +46,7 @@
 #include <sys/zfs_znode.h>
 #include <sys/zvol.h>
 #include <linux/blkdev_compat.h>
+#include <linux/delay_compat.h>
 
 unsigned int zvol_inhibit_dev = 0;
 unsigned int zvol_major = ZVOL_MAJOR;
@@ -1331,6 +1332,9 @@ __zvol_snapdev_hidden(const char *name)
 	(void) strlcpy(parent, name, MAXPATHLEN);
 
 	if ((atp = strrchr(parent, '@')) != NULL) {
+		printk(KERN_INFO "ZFS: sleeping for some time here\n");
+		msleep(30 * 1000);
+		printk(KERN_INFO "ZFS: ok, waking up\n");
 		*atp = '\0';
 		error = dsl_prop_get_integer(parent, "snapdev", &snapdev, NULL);
 		if ((error == 0) && (snapdev == ZFS_SNAPDEV_HIDDEN))
@@ -1354,6 +1358,8 @@ __zvol_create_minor(const char *name, boolean_t ignore_snapdev)
 
 	ASSERT(MUTEX_HELD(&zvol_state_lock));
 
+	printk(KERN_INFO "ZFS: hello from __zvol_create_minor! minor name: %s\n", name);
+
 	zv = zvol_find_by_name(name);
 	if (zv) {
 		error = SET_ERROR(EEXIST);